1. Field of the Invention
The present invention relates to a printing apparatus using a line type thermal head for printing on a recording sheet such as a thermal paper or thermal transfer sheet, capable of automatically detecting a defect of the thermal head, and a communication apparatus and an information processing apparatus, provided with the same.
2. Description of the Related Art
Conventionally, in a printing apparatus which uses a thermal head to print on a recording sheet, there has been a problem that when a defect occurs in the thermal head, respective heaters of the thermal head generate heat, and a trouble such as destruction or burnout of the thermal head occurs. When such a trouble occurs, a serious influence is exerted also on a printed image. In view of such a problem, for the purpose of confirming the quality of a printed image, a method in which a current is made to flow through a thermal head during printing or at the point of time when the thermal head is not used, for example, immediately before the printing, and a defect of the thermal head is detected through the value of the current, is known as a well-known technique.
Besides, a method of detecting a defect of a thermal head or preventing a trouble is disclosed in, for example, Japanese Unexamined Patent Publications JP-A 63-227356 (1988), JP-A 63-145058 (1988), JP-A 3-193367 (1991), JP-A 7-9691 (1995), or JP-A 11-254722 (1999).
JP-A 63-227356 discloses a method in which an inspection signal as data is inputted to a thermal head which is divided into a plurality of parts of data by a plurality of strobe signals which sections of data are printed in different printing timings, blocks divided by the plurality of strobe signals are forcibly turned on, a power source of the thermal head is switched to an inspection power source line, and currents flowing through respective heaters are detected, so that a defect of the thermal head is detected.
JP-A 63-145058 discloses a method in which a current flowing through a thermal head is detected at every printing line, the detection current is compared with a reference value set in accordance with a thermal head current corresponding to the minimum number of printing dots per line, defect detection of the thermal head is carried out through the number of lines at which the value of the detection current exceeds the reference value, and the quality of printing is judged.
JP-A 3-193367 discloses a method in which a current flowing through a thermal head in a time other than a printing time is detected by a voltage drop through a resistor provided in a supply power source of the thermal head, and when abnormality is detected by detection means, the supply power source is turned off.
JP-A 7-9691 discloses a method in which dot information for specifying at least one heater used for abnormality detection is generated, electric power is supplied from a power source to only the heater used for abnormality detection, and a voltage drop of the heater supplied with the electric power is compared with a threshold voltage so that abnormality is detected.
JP-A 11-254722 discloses a method in which when first power supply means does not supply electric power for printing, second power supply means supplies electric power for detection to a thermal head through failure detection means, and defect detection of the thermal head is carried out based on a current flowing through at least one heater.
However, in the publication, in the case where defect detection of the thermal head is carried out during the printing, a specific procedure for interrupting the printing and for detecting a defect of the thermal head is required. Besides, the detection of the defect of the thermal head is carried out during the printing or immediately before the printing. Accordingly, it is impossible to detect such a trouble that for example, the thermal head suddenly fails in a state where printing is not made, or a control program is out of control, and a current flows through the thermal head in a time other than a printing time to cause heat generation with a heater, so that destruction, burnout or the like of the thermal head occurs.
An object of the present invention is to provide a printing apparatus using a thermal head in which defect detection of the thermal head is carried out during printing by a simple method without interrupting the printing and the thermal head is always monitored with respect to abnormality over a period including a printing time and a waiting state, to prevent a trouble such as destruction and burnout of the thermal head, and a communication apparatus and an information processing apparatus, provided with the same.
The invention provides a printing apparatus comprising:
a line type thermal head having a heater array composed of a plurality of heaters, for printing on a recording sheet; and
defect detection means for, in the case where print data to cause all of one line to be blank is inputted to the thermal head, detecting a defect of the thermal head based on a current flowing through each heater at a time of printing of the blank line.
Since the thermal head prints by heat generation, if a defect occurs in the thermal head, abnormality occurs in a printed image, and the thermal head generates heat, so that the trouble such as destruction and burnout of the thermal head can occur. According to the invention, in the case where the print data to cause all of one line to be blank is inputted to the thermal head at the time of the printing, the defect of the thermal head can be detected based on the current flowing through each heater. Accordingly, the defect of the thermal head can be detected during the printing without interrupting the printing.
In the invention it is preferable that print data for one line is divided into a plurality of parts of data by strobe signals which parts of data are printed in different print timings, and defect detection of the thermal head is carried out for respective blocks divided by the strobe signals.
According to the invention, the print data is divided into the plurality of parts of data by the strobe signals, and defect detection of the thermal head can be carried out for each block of the thermal head. Accordingly, a defect portion of the thermal head can be specified. Besides, since the element number of the heaters detected at the same time becomes small, even if leak currents of drive circuits of the respective heaters are accumulated, the influence on the detection of the defect of the thermal head becomes weak.
Besides, the invention is characterized in that the defect detection means comprises a resistor which is interposed in a power source line of the thermal head and detects a current supplied to the thermal head when print data to cause all of one line to be blank is inputted to the thermal head, and a circuit for short-circuiting the resistor in the case where all of one line is not blank.
According to the invention, in the defect detection means, in the case where the print data to cause all of one line to be blank is inputted to the thermal head, the current supplied to the thermal head is detected by the current detection resistor interposed in the power supply line of the thermal head, and in the case where the print data not to cause all of one line to be blank is inputted to the thermal head, the current is supplied to the thermal head through the circuit for short-circuiting the resistor. The circuit for short-circuiting the current detection resistor can prevent the current applied to each heater from being changed by the voltage drop at the current detection resistor.
Besides, the invention is characterized in that the defect detected by the defect detection means is classified into a plurality of stages in accordance with the stage of the defect, a processing after defect detection is also classified into a plurality of stages made of a combination of an alarm occurrence and a printing stop, and a processing classification after the defect detection is assigned in accordance with the classification of the defect.
According to the invention, the defect detected by the defect detection means is classified into, for example, three stages in accordance with the stage of the defect, and the alarm of the trouble of the thermal head is issued at the respective stages to notify the user, and at the same time, when the stage of the trouble is raised, for example, the printing is automatically stopped, so that it is possible to prevent the trouble such as the poor quality of a printed image and the fatal destruction and burnout of the thermal head caused by the heat generation of the heater.
Besides, according to the invention, defects detected by the defect detection means are classified into the plurality of stages in accordance with levels of the defect, the measures after the defect detection are also classified into the plurality of stages composed of combinations of alarm occurrence and printing stop, and assignment of measure classification after the defect detection is carried out in accordance with the classification of defects, so that it is possible to prevent the trouble such as poor quality of printed image and the fatal destruction and burnout of the thermal head caused by heat generation of the heater.
In the invention it is preferable that in the case where print data to cause all data of one line to be blank is not inputted to the thermal head with respect to a predetermined printing amount, or every predetermined printing amount, print data to cause all of one line to be blank is forcibly inserted.
According to the invention, when the printing amount, for example, the number of pages, the number of lines, or the length of printing (the number of characters) is predetermined, and when printing of the printing amount is carried out, the print data to cause all of one line to be blank is forcibly inserted. Alternatively, the blank data of one line is inserted every predetermined printing amount, for example, in the first line of every page, irrespective of whether or not all of one line is blank. Accordingly, even in the case where the print data to cause all of one line to be blank does not exist in an image to be printed, the defect of the thermal head can be certainly detected.
In the invention it is preferable that when the print data to cause all of one line to be blank is forcibly inserted, a recording sheet is not advanced in printing of this line.
According to the invention, the recording sheet such as a thermal paper or a thermal transfer paper is not advanced with respect to the line in which the print data to cause all of one line to be blank is forcibly inserted. Accordingly, even if the print data to cause all of one line to be blank is forcibly inserted, the blank line is not printed.
The invention provides a printing apparatus comprising:
a line type thermal head having a heater array composed of a plurality of heaters, for printing on a recording sheet; and
defect detection means for, over a period including a printing time and a waiting state, detecting a current flowing through the thermal head by inserting print data to cause all of one line to be blank each time when a predetermined time elapses, or detecting the current flowing through the thermal head at a point of time when a strobe signal is not inputted, and detecting a defect of the thermal head based on the detected current.
According to the invention, the defect of the thermal head can be detected each time the predetermined time elapses over the period including not only the printing time but also the waiting state. Accordingly, since the defect of the thermal head can always be detected irrespective of the printing, it is possible to prevent the trouble such as destruction and burnout of the thermal head caused by the heat generation of the heater.
In the invention it is preferable that when the detection means detects the defect of the thermal head, a current to the thermal head is cut off.
According to the invention, when the defect detection means detects the defect of the thermal head, the current to the thermal head is cut off, so that it is possible to prevent the trouble such as destruction and burnout of the thermal head caused by the heat generation of the heater in advance.
The invention provides a communication apparatus comprising the above-mentioned printing apparatus.
Besides, the invention provides an information processing apparatus comprising the above-mentioned printing apparatus.
According to the invention, the printing apparatus can be used for the communication apparatus such as a facsimile or the information processing apparatus such as an Internet facsimile.